Studies of the progressive development of a malignant phenotype of a carcinogen initiated cell have been presented. For comparative purposes, stages in the progression have been identified where both carcinogen initiated cells and cells isolated from human squamous cell carcinoma (SCC) exhibit similar characteristics. Restrictions we faced in the past in the identification of cells in these stages have been overcome by the preparation of monoclonal antibodies (MoAb) that specifically identify these characteristics. These different MoAb's were prepared against specific cell surface antigens, phenotypic markers for normal cells, tumor cells, and keratin. Our current interest is to investigate how the tumor cells or carcinogen initiated cells progress from a normal phenotype to a malignant phenotype. Tumorigenicity, a natural endpoint for these studies, will be the stage of interest to investigate. We will: examine how the carcinogen initiated cells progress towards a neoplastic phenotype; isolate and separate tumor cell phenotypes that exhibit differences in cell surface antigens that are characteristic of changes in the cells as they progress from stage to stage; characterize the expression of intermediate keratin filaments in the tumor subpopulations that are in the different stages; prepare genomic DNA from tumor cell populations that exhibit LIG and tumorigenicity and compare the stages in the progression. A comparison of carcinogen initiated human epithelial cells with tumor cells with similar phenotypic characteristics will be undertaken using transfection technology and the progression from stage in the development of a malignant phenotype will be investigated. Moreover, an understanding of how malignant phenotypes lose specific cellular characteristics will be examined with molecular and specific phenotypic probes and the information gathered will aid us in understanding multistage carcinogenesis in a human model system.